The operation to drive Isil fighters from Mosul is proceeding ahead of schedule, according to Iraqi and US authorities, as fighting continued in the city's eastern suburbs on Thursday.

Members of Iraq's elite counter terrorism forces reported they were advancing towards the centre of Mosul after breaching the eastern outskirts of the city for the first time since it was overrun by fighters from the Islamic State of iraq and the Levant in 2014 on Tuesday.

The US Special Presidential Envoy for the Global Coalition to Counter ISIL Brett McGurk hailed Iraqi forces entering the eastern suburbs of Mosul as a milestone, writing on Twitter on Thursday: “Ways to go, but ahead of schedule.”

“The plan of the join command in Nineveh is going faster than we planned,” Iraq's Interior Ministry spokesman Brigadier Saad Maan told local news outlet Rudaw in a televised interview. Protecting civilian lives and infrastructure were priorities that could slow their advance, he said.

Milestone: Iraqi forces enter eastern neighborhoods of #Mosul this morning. New advances on all axes. Ways to go, but ahead of schedule.

“Militarily we are sure of the success of our operation, it's just a matter of time.”

The head of counter terrorism forces Abd al-Ghani al-Asadi has said that “In the coming hours, we will enter other neighbourhoods of Mosul,” local media reported.

As the fighting has reached populated areas of Mosul, the number of civilians fleeing the violence has increased.

The International Organization for Migration's Iraq mission reported on Thursday that nearly 21,000 have been displaced since the operation began on October 17, with nearly 1000 fleeing in the past 24 hours alone.

Iraqi families, who fled the violence due to the ongoing operation by Iraqi forces against jihadists of the Islamic State group to retake the city of Mosul, board a truck before heading to camps housing displaced peopleCredit:
BULENT KILIC/AFP/Getty Images

The United Nations fears that more than a million Iraqis could eventually be displaced during the operation.

As winter approaches, inclement weather may soon slow operations. Iraqi special forces paused their advance inside Mosul on Wednesday due to rain and sandstorms, which can hinder international coalition jets from providing air support.

To the west of Mosul Shia militias have continued advancing towards the town of Tel Afar. The predominantly Turkmen town is strategically located between Mosul and the Syrian border.

"We are about 15 kilometres from Tel Afar,” said PMU spokesperson Ammar Al Musawi. “We are just waiting for orders to go inside.”

Fire fighters try to extinguish the fire at oil wells, were set on fire by Isil as they fled after Al Qayyarah town was liberatedCredit:
Yunus Keles/Anadolu Agency/Getty Images

He called on Isil supporters to fight the "enemies of God" and for the suicide fighters to "turn the nights of the unbelievers into days, to wreck havoc in their land and make their blood flow as rivers."

Baghdadi did not refer directly to Mosul in the audio statement released to his followers. It was not clear when it was recorded but it referred to recent events.

Baghdadi's location has been the subject of speculation since he suffered a spinal injury in an air strike last year.

Foreign Secretary Boris Johnson said intelligence suggested that Baghdadi had "vacated the scene", but he did not say where the Isil leader might be.